This invention relates to fluid diffusers, and particularly to an improved diffuser that is useful for introducing bubbles of air into wastewater to be treated.
In the aeration treatment of wastewater, it is common to introduce the air through a series of submerged diffusers mounted at spaced positions along the length of a manifold pipe. The diffusers have apertures through which the air can escape, preferably as small bubbles. A common type of diffuser uses a rubber or rubber-like flexible diaphragm working against a flat, rigid disc. When air is not being admitted to the diffuser, the flexible diaphragm seats against the hard disc under the pressure of the water and seals the air openings. When air is admitted under pressure, the flexible diaphragm moves away from the disc and opens the apertures to allow the air to escape.
One form of flexible diaphragm diffuser is disclosed in U.S. Pat. No. 3,525,436 issued Aug. 25, 1970 to D. J. Reckers for "Sewage Treatment Plant." In the diffuser of that patent, the rigid disc has a series of holes located inwardly of its perimeter. The flexible diaphragm overlays the top surface of the disc and is joined to the perimeter of the disc by a clamp. When air is introduced under pressure through a central opening in the disc, the diaphragm is unseated and air can pass out the bottom through the holes in the disc. Another form of diaphragm diffuser traps the diaphragm between the top surface of the disc and an upper retaining ring. When air under pressure is admitted through a central disc opening, the diaphragm moves off of the top of the disc and air can escape radially outwardly between the disc and the diaphragm.
Still another form of diaphragm diffuser uses no clamp or retainer ring but instead relies upon the resiliency of the diaphragm to hold it to the rigid disc. In this version, the rigid disc has a scalloped perimeter which is grasped by a rim of the diaphragm. Holes are provided in the diaphragm and the holes are closed until the diaphragm is moved away from the disc when air is admittted through a central opening in the disc.
One problem encountered by all such air diffusers is the potential build-up of deposits in the air openings, particularly when hard water is treated. The resulting calcium deposits can partially close the air passages if the operation of the diffuser does not tend to cause the calcium deposits to be physically broken up or if the direction of air travel through the openings is such that not all surfaces of the openings are scoured by the passing air. Also, in those diaphragm diffusers which do not provide a separate retainer or clamp for joining the diaphragm to the rigid disc, the diaphragm can be blown loose of the disc. This danger increases after the air passages have become partly clogged because of the resulting increase in the air pressure against the diaphragm.
A diffuser in accordance with the present invention provides a simple but efficient mechanism for introducing air or other fluid into a liquid or other fluid. Discrete air openings are defined between the perimeter of the disc and a perimeter of the diaphragm, so that the flexing of the diaphragm will help to dislodge calcium deposits and a desirable direction of air travel through the passages will scour the entire passage. The diffuser is also self-regulating in that increased air pressure will tend to decrease the size of the air openings. At the same time, the diffuser exhibits improved anchoring of the diaphragm to the disc without the need for a separate clamp or retainer.